incomplete text messages

Hi I got a new Droid at Christmas and have been having issues with sending text messages. Some of the messages that I have sent are recieved as incomplete. This does not happen to everyone in fact most people I can text without any problem. It consistantly seems to be the same people that recieve half of my message. It has nothing to do with the length of the message as I have sent messages with only one word and they are still recieved as incomplete. I would appreciate any help with this issue. I should also mention that I have already been back to the store several times and I have already had the phone replaced by another phone. The same issue is still happening! HELP!!!

Well I could see it if it were just one person having trouble reading my texts but would at least 4 people all be having trouble with their phones? And they are not having this issue with recieving texts from other people just my phone. But I certainly thank you for taking the time to reply!

No I haven't used the automatic task killer; but I have not loaded a single app or game on the phone. The weird thing is one day I had a conversation back and forth with a friend, about 20 texts and the next day I sent a text to the same person and all my texts were incomplete. So it's very random. That's the way it's been going sometimes it's fine and other times it's not.
The people at the Verizon store are completly baffled!